Insiders tell Us that the actress, 27, and her tennis pro beau, 26, plan to tie the knot on Dec. 31 in Southern California. The event will double as a fire-and-ice-themed holiday bash, with cocktails, dancing, and plenty to celebrate.

The actress' rep first confirmed her engagement to Us Weekly on Sept. 26, just three months after the couple started dating, and just a few days after they made their red-carpet debut together at a pre-Emmys party. "I know that it seems a little crazy on paper," she told ET after Sweeting proposed. "But it's what works for us."

Earlier this month, the blonde star joked on The Late Late Show With Craig Ferguson that she had been planning her wedding for 27 years. "I might ride in on one of my horses," she quipped. "I secretly kinda want to do that."

What she wants more than anything, though, is for the big day to mean something. "I only want to do this once," she said.